This invention relates to a process for preparing carboxylic acids from olefins in the presence of a catalyst and more particularly relates to a process for preparing carboxylic acids wherein greater than 50 mole percent of the carboxylate groups are at the terminal position from an olefin wherein greater than 50 mole percent of the olefin has unsaturation at other than the terminal position.
Natural fatty acids, wherein the carboxylate group is virtually always at the terminal position of the alkyl chain, are widely used in industry for a variety of applications. The lower molecular weight fatty acids, such as those containing 6 to 10 carbon atoms, are used as intermediates to form plasticizers, surfactants or lubricants and in many other important uses in today's society. The higher molecular weight fatty acids, such as those containing an average of about 12 carbon atoms, are widely used in the preparation of toilet bar soaps. Millions of pounds of these natural fatty acids are consumed in the United States each year.
There is a need, however, to supplement the source of supply of these natural fatty acids and accordingly synthetic fatty acids produced from olefins are being used to supplement or even replace the natural products. However, in order to use synthetic fatty acids, in many applications it is necessary that the synthetic fatty acid have the carboxylate group at the terminal carbon atom.
The preparation of synthetic fatty acids by the reaction of olefins, carbon monoxide and water using a number of catalysts, such as a cobalt catalyst, is well known. As an example, U.S. Pat. No. 3,661,957 and U.S. Pat. No. 3,678,083 disclose processes for preparing carboxylic acids from higher olefins, say those having 10 or more carbon atoms in the olefin chain, carbon monoxide and water using a cobalt catalyst and a pyridine promoter. The prior art also discloses that the linearity of the acid product decreases with increasing temperature (see for example, P. Pino et al "Isomer Distribution in Products of Olefin Hydroformylation and Other Carbonylation Reactions", La Chimica e L'Industria, Vol. 50, No. 1, January 1968, pages 106-118).
Although satisfactory results are obtained using these and other processes in the prior art, the prior art processes fail to achieve the advantages of the present invention in one or more respects. Although temperatures of up to 180.degree. C., preferably in the range of 140.degree. to 160.degree. C., are used with pyridine-type promoters and a cobalt catalyst, prior art processes teach that in order to obtain a carboxylic acid wherein most of the carboxylate groups are at the terminal position, it is necessary to use a feed of mostly alpha-olefin, which can be obtained only through special processing and is generally more expensive.
Now, according to the present invention, a process for preparing carboxylic acids wherein greater than 50 mole percent of the carboxylate groups are at the terminal position has been developed using an olefin feed that can contain as little as 10 percent or less of alpha-olefin by reaction at higher temperatures, all of which is contrary to the teachings of the prior art. Since the alpha-olefins are far more expensive as a feed material to the carboxylation process using carbon monoxide and water, those skilled in the art will recognize that there is a clear advantage to the process of the present invention.